Bogle, H.J. 2014

377 Pages·2015·14.24 MB·English

Neuropathological and Molecular Studies
in Alpers’ Syndrome

Helen Judith Bogle B.Sc. (Hons)

A thesis submitted for the degree of Doctor of Philosophy

Wellcome Trust Centre for Mitochondrial Research

Institute for Ageing and Health

May 2014
Author’s Declaration
This thesis is submitted to the degree of Doctor of Philosophy in the University of
Newcastle. The research was performed in the Wellcome Trust Centre for
Mitochondrial Research under the supervision of Professor D.M. Turnbull, Professor
R.W. Taylor, and Dr R McFarland, and is my own work unless otherwise stated in the
text.
I certify that none of the material offered in this thesis has been previously submitted by
me for a degree or any other qualification at this or any other university.

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Abstract
Abstract
Mitochondrial disease is a significant burden on human health, at least 16.5 in 100,000
individuals are at risk of developing a mitochondrial DNA disorder (Schaefer et al.,
2008). Early-onset mitochondrial disease affects young children and can have
devastating consequences. One such disease, Alpers’ syndrome, is a rare, autosomal
recessive, early-onset neurological condition, which was first described in 1931 (Alpers
1931), characterised by refractory seizures, developmental delay, ataxia, visual
abnormalities, and liver dysfunction and failure (Huttenlocher et al., 1976). It is primarily
attributable to mutations in the gene POLG which encodes the only known polymerase
to replicate mitochondrial DNA (Hance et al., 2005). POLG mutations lead to
secondary defects of mitochondrial DNA (mtDNA), including deletion and depletion.
There is a poor prognosis for patients diagnosed with Alpers’ syndrome with no
effective treatments currently available and little research into this rare condition.
The research presented here aims to understand the mechanisms leading to the
neuropathological characteristics and clinical features in 12 patients with Alpers’
syndrome and sex-/age-matched controls. Four brain areas were investigated; three
areas frequently reported to show involvement in Alpers’ syndrome and one area that
is less frequently described. A battery of immunohistological stains and antibodies was
used to assess the cohort. Neuropathological features identified and quantified
included severe neuronal loss, widespread astrogliosis, reduced mitochondrial mass,
white matter abnormalities, and microglial activation. The most severe neuropathology
occurred in the posterior regions of the brain, yet all areas investigated exhibited
pathology to different degrees. The expression of key respiratory chain proteins was
quantified in neurons from different brain regions and revealed wide variation within
and between individuals. There was a clear deficiency of complexes I and III in
neurons, with a milder deficiency of complex IV. Assessment of mtDNA content in
neurons revealed prominent mtDNA depletion, with a subset of neurons in older
patients displaying high levels of mtDNA deletion.
This study shows clear evidence of respiratory chain deficiency of complexes I and III.
This occurs most severely in the posterior region of the brain, correlating with more
neuropathological changes in these regions. MtDNA depletion is a central feature of
DNA damage in neurons likely driving the development of respiratory chain deficiency.
These findings provide a clear insight into the mechanisms of respiratory chain
deficiency leading to the neuropathology and clinical features in patients with Alpers’
syndrome.
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Abstract

Alpers, B. J. (1931). "Diffuse progressive degeneration of the gray matter of the
cerebrum." Arch Neurol Psychiatry 25: 469-505.
Hance, N., M. I. Ekstrand and A. Trifunovic (2005). "Mitochondrial DNA polymerase
gamma is essential for mammalian embryogenesis." Human Molecular
Genetics 14(13): 1775-1783.
Huttenlocher, P. R., G. B. Solitare and G. Adams (1976). "Infantile diffuse cerebral
degeneration with hepatic cirrhosis." Archives of Neurology 33(3): 186-192.
Schaefer, A. M., R. McFarland, E. L. Blakely, L. He, R. G. Whittaker, R. W. Taylor, P.
F. Chinnery and D. M. Turnbull (2008). "Prevalence of mitochondrial DNA
disease in adults." Annals of Neurology 63(1): 35-39.

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Acknowledgements
Acknowledgments
First and foremost, I would like to thank the patients involved in this study and their
families. The generosity shown by the families in being a part of this study is greatly
valued.
I would like to thanks the project’s sponsors: The Ryan Stanford Appeal and The Sir
James Knott Trust. The Ryan Stanford Appeal has been an inspiration, in their
optimism and in determination. Anne and Dave Stanford have worked tirelessly to
ensure this project went ahead and maintain its funding, and without Ryan Stanford,
none of this would have been possible in the first place.
I would like to thank everyone in the MRG for their help and advice and thank the
NBTR for their help with samples and techniques. I would particularly like to thank my
supervisors for all their support, encouragement and advice throughout this project,
and thank Dr Evelyn Jaros for all her help with examining the slides and pathology
discussions. A special ‘thank you’ goes to Dr Nichola Lax for all her support throughout
this project, from beginning to end. She showed me incredible patience and practical
help whenever it was needed, and I am extremely grateful. Being a part of the MRG
has given me a lot of support and guidance, and the best thing about working with a
group of scientists who love to bake – there is always a lot of cake!
Finally, I need to say a huge thank you to all my friends and family, who have shown
me so much support and patience over the last three years. My mum and dad have
been there at every step, supported me through the write-up period, and somehow
been persuaded to proofread drafts of chapters as well. I am very grateful for their love
and support. I cannot thank all my friends enough for the endless cups of coffee and for
making me laugh through the tough times.

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